The lung is composed of at least four collagen types. Type 1 (alpha 1 (I)2 alpha 2) is the fibrillar collagen found in the parenchyma and blood vessels. Type II ((alpha 1 (II))3) is cartilage collagen of the tracheo-bronchial tree. Type III ((alpha 1 (III))3) is probably reticulin found in the parenchyma and around blood vessels. Type IV ((alpha 1 (IV))3) is probably basement membrane collagen, but it has not as yet been fully characterized. Methods are being developed to quantitate Types I and III collagen in lung parenchyma and cell culture in order to help understand the control of lung collagen in health and disease.